Glad you think this is amusing Nick, bet it's not for Sandy.
I would suggest the problem with you sounder is a known problem with the old Risco Nova box, bet you've got one of these.
There is a 'fix' from Risco but its is a get the ladder out and alter the SA PCB, not the job for Joe public.
Afraid you need an alarm company Sandy, good luck
acorn
January 2010